JUBA, South Sudan (AP) — A small plane crashed in a remote part of South Sudan, killing at least 18 people on Wednesday, an official said.

The flight, chartered by Chinese oil firm Greater Pioneer Operating Co., had 21 people on board, including two pilots, said Gatwech Bipal, the minister of information in the oil-rich Unity state, where the crash happened earlier on Wednesday.

The plane crashed while it was taking off near an oil field to head to the international airport in Juba, the South Sudanese capital, he said.

It wasn't immediately clear what caused the crash, and authorities hadn't yet revealed the identities of the victims. Local media reported that the plane was carrying oil workers.

South Sudan, which gained independence from Sudan in 2011, is a major oil producer in the region. The East African nation has been trying to ramp up oil production and exports amid persistent cashflow issues for the government.